[3.13] gh-123083: Fix a potential use-after-free in ``STORE_ATTR_WITH… (#123235)

[3.13] gh-123083: Fix a potential use-after-free in ``STORE_ATTR_WITH_HINT`` (gh-123092)
(cherry picked from commit 297f2e093e)

Lib/test/test_dict.py

@@ -1476,6 +1476,24 @@ class DictTest(unittest.TestCase):
         gc.collect()
         self.assertTrue(gc.is_tracked(next(it)))
 
+    def test_store_evilattr(self):
+        class EvilAttr:
+            def __init__(self, d):
+                self.d = d
+
+            def __del__(self):
+                if 'attr' in self.d:
+                    del self.d['attr']
+                gc.collect()
+
+        class Obj:
+            pass
+
+        obj = Obj()
+        obj.__dict__ = {}
+        for _ in range(10):
+            obj.attr = EvilAttr(obj.__dict__)
+
     def test_str_nonstr(self):
         # cpython uses a different lookup function if the dict only contains
         # `str` keys. Make sure the unoptimized path is used when a non-`str`

Misc/NEWS.d/next/Core_and_Builtins/2024-08-17-17-26-25.gh-issue-123083.9xWLJ-.rst

@@ -0,0 +1 @@
+Fix a potential use-after-free in ``STORE_ATTR_WITH_HINT``.

Objects/dictobject.c

@@ -1762,6 +1762,8 @@ insert_split_value(PyInterpreterState *interp, PyDictObject *mp, PyObject *key,
         uint64_t new_version = _PyDict_NotifyEvent(interp, PyDict_EVENT_MODIFIED, mp, key, value);
         STORE_SPLIT_VALUE(mp, ix, Py_NewRef(value));
         mp->ma_version_tag = new_version;
+        // old_value should be DECREFed after GC track checking is done, if not, it could raise a segmentation fault,
+        // when dict only holds the strong reference to value in ep->me_value.
         Py_DECREF(old_value);
     }
     ASSERT_CONSISTENT(mp);

Python/bytecodes.c

@@ -2170,14 +2170,15 @@ dummy_func(
                 new_version = _PyDict_NotifyEvent(tstate->interp, PyDict_EVENT_MODIFIED, dict, name, value);
                 ep->me_value = value;
             }
-            Py_DECREF(old_value);
-            STAT_INC(STORE_ATTR, hit);
             /* Ensure dict is GC tracked if it needs to be */
             if (!_PyObject_GC_IS_TRACKED(dict) && _PyObject_GC_MAY_BE_TRACKED(value)) {
                 _PyObject_GC_TRACK(dict);
             }
-            /* PEP 509 */
-            dict->ma_version_tag = new_version;
+            dict->ma_version_tag = new_version; // PEP 509
+            // old_value should be DECREFed after GC track checking is done, if not, it could raise a segmentation fault,
+            // when dict only holds the strong reference to value in ep->me_value.
+            Py_DECREF(old_value);
+            STAT_INC(STORE_ATTR, hit);
             Py_DECREF(owner);
         }
 

Python/generated_cases.c.h

@@ -5608,14 +5608,15 @@
                 new_version = _PyDict_NotifyEvent(tstate->interp, PyDict_EVENT_MODIFIED, dict, name, value);
                 ep->me_value = value;
             }
-            Py_DECREF(old_value);
-            STAT_INC(STORE_ATTR, hit);
             /* Ensure dict is GC tracked if it needs to be */
             if (!_PyObject_GC_IS_TRACKED(dict) && _PyObject_GC_MAY_BE_TRACKED(value)) {
                 _PyObject_GC_TRACK(dict);
             }
-            /* PEP 509 */
-            dict->ma_version_tag = new_version;
+            dict->ma_version_tag = new_version; // PEP 509
+            // old_value should be DECREFed after GC track checking is done, if not, it could raise a segmentation fault,
+            // when dict only holds the strong reference to value in ep->me_value.
+            Py_DECREF(old_value);
+            STAT_INC(STORE_ATTR, hit);
             Py_DECREF(owner);
             stack_pointer += -2;
             DISPATCH();